1. Field of the Invention
The present invention relates to an STM(Synchronous Transfer Mode)-16 Network-Node Interface(NNI) and the fault diagnosing method thereof, which is speedily capable of checking whether a fault is occurred at a local station or a remotely located destination station during the data communication between the destination station and the local station, thereby processing the fault location to achieve an improved operation and maintenance of the STM-16 NNI on-demand.
2. Description of the Prior Art
There have been proposed various apparatuses and methods for channel dual switching of multiplex sections. One of examples has been introduced to alleviate phase difference invoked by different phase delay based on a difference between two paths; and to minimize data loss and duplication induced by a frame delay difference between the two paths during a channel switching, when Network-Node Interface(NNI) frames is transmitted via the two different paths in the multiplex section, to thereby prevent instantaneous disconnection from entailing(See, Japanese Patent Application No. 5-23520). In another, a switching information transmitting method and channel switches, as described in Japanese Patent Application No. 5-321757, has been introduced to implement auto-switching at terminals of two multiplex sections, by transmitting automatic-protection switching bytes K1 and K2 on Section Overheads(SOH) through Path Overhead(POH); transforming the bytes K1 and K2; and transmitting the bytes to different stations.
The multiplex section protection(MSP) functions, at the ends of a multiplex section, make requests for and give acknowledgements of switch action by using the MSP bytes that are K1 and K2 bytes. The K1 byte indicates a request of a channel for switch action. Bits 1-4 of the byte indicate the type of request and bits 5-8 indicate the number of the channel which is to be protected. In ITU-T Recommendation G.783, there are 4 unused values in the types of request. The STM-16 signal consits of sixteen VC-4 AUGs or four VC-4-4C AUGs.
In the conventional approaches, however, when an error is generated at each dependent AUG signal contained in the multiplex sections, since the error information must be transmitted through the Path Overhead, it is difficult to transfer information to other station when corresponding path has a fault.
Referring to a reference published by B. Edmaier, W. Fischer, A. Klug, Siemens, entitled "Alignment Server for Hitless Path-Switching in ATM Networks, ISS'95, Germany", VP/VC alignment server(VAS) has been introduced to constrain the loss of ATM cells and data duplication depending on a delay difference between two paths from causing, during path-switching in Asynchronous Transfer Mode(ATM) networks, by synchronizing the two paths during the switching, on-demand.
However, The VAS described above suffers from the disadvantage that even if it is capable of detecting a fault state. i.e., the state of a received signal and a transmitted signal during the generation of the fault, but it is difficult to check whether any station has the fault.
In the conventional approaches, the fault state and its degree of multiplexed AUG transmitted on the STM-16 frame through the Section Overhead(SOH) and the Path Overhead(POH) thereof are detected, and informed to the destination station. However, it suffers from the disadvantage that it is difficult to correctly discriminate the fault location occured, and further, the error on the Path Overhead may be determined as a path fault due to the hindrance of a circuit incorporating therein, thereby leading to the degradation in reliability.
In addition, when a fault is generated in an AUG signal during the data transmission and reception, boards installed on both the destination and local stations should be alternatively exchanged for new boards until the state of the transmission and reception is normal, which may, in turn, lead to degrade the efficiency in operation and maintenance applications.